/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/Operations/GeodesicPath.h
segment ID of a new segment inserted before the specified existing segment. If SegmentIDToInsertBefore is InvalidID, then insert at head
int32 InsertSegmentBefore ( const [FDirectedSegment](API\Plugins\DynamicMesh\Operations\FEdgePath\FDirectedSegment) & DirectedSegment, int32 SegmentIDToInsertBefore )